[Emission of Methane from a Key Lake in the Eastern Route of the South-to-North Water Transfer Project and the Corresponding Driving Factors].

ABSTRACT

Lakes play an important role in the biogeochemical cycling of dissolved organic matter (DOM) and the emission of methane (CH4). We investigated the concentration and effluxes of CH4 and then analyzed the corresponding driving factors in Lake Luoma, a key lake along the South-to-North Water Transfer Project. Our results indicated that Lake Luoma was a hotspot of CH4 emissions with an annual mean concentration and efflux of (0.12±0.09) µmol·L-1 and (21.0±18.5) mmol·(m2·d)-1, respectively. We found higher mean CH4 levels in the wet season than those in the dry season and further higher levels than those in the wet-to-dry transition season. Spatially, the CH4 efflux was higher in the northwest inflowing regions and lower in the southeast outflow regions. The variability in annual CH4 efflux was affected by a combination of water temperature and hydrological conditions. Terrestrial input of dissolved organic carbon (DOC) and chromophoric DOM (CDOM) had fueled the production of CH4 by providing necessary carbon substrates, and four PARAFAC DOM components were identified including a microbial humic-like C1, a tryptophan-like C2, a terrestrial humic-like C3, and a tyrosine-like C4. The CH4 efflux from the lake was significantly promoted by the input and accumulation of terrestrial humic-like components, and Chl-a had no correlation with CH4 efflux, suggesting that algal degradation was not directly fueling the emission of CH4. Lake Luoma had been significantly disturbed by human activities, and terrestrial input of nutrient loading (TN and TP) into the lake not only improved the productivity and trophic level of the water body but also enhanced the production and release of CH4 from the surface water. We concluded that the CH4 emissions in Lake Luoma can be influenced by the combination of environmental factors, CDOM composition, and nutrient level. Long-term observation is needed for better evaluation of the driving factors in fueling the emission of CH4 so as to effectively reduce the emissions of CH4 and other greenhouse gases by taking corresponding countermeasures.